This project involves a biochemical and biological study of defective interfering (DI) particles of animal and human viruses. Vesicular Stomatitis virus is being employed as the primary model system because of the ready purification of its T particles. We are also attempting to extend information from the VSV system to other viruses such as measles, rabies, mumps, poliovirus, etc. This project has 2 major goals. One is to understand the generation and interfering mode of action of DI particles at biochemical and cell levels. The second major goal is to explore the influence of DI particles upon the course of acute and slow virus infections in vivo in animal hosts. The prophylactic and vaccine potential of DI particles is also being explored in vivo in animal hosts.